Method and apparatus for varying developer bandwidth

ABSTRACT

An electrostatic copying machine is provided utilizing a magnetic brush development system. The magnetic brush presents a band of developer to a latent electrostatic image, the width of the developer band being changed in accordance with the size of copy paper used. This is effected by utilizing a variable length magnet inside a non-magnetic rotatable roller which carries developer thereon. The length of the magnet is varied in accordance with the size of the copy paper used to accordingly change the length of the magnetic field emanating therefrom thereby effecting a corresponding change in the bandwidth of the developer transported to the image. An alternate method for effecting the same result is to utilize a shunt which may be swung into a position surrounding one end of the magnet to prevent the magnet field emanating from that end of the magnet from being effective to attract developer to the roller thereby decreasing the developer bandwidth.

United States Patent 11 1 Hudson METHOD AND APPARATUS FOR VARYINGDEVELOPER BANDWIDTH Frederick W. Hudson, West Henrietta, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Apr. 29, 1974 [2]] Appl. No.: 464,864

[75] Inventor:

521 U.S. c1 118/637; 117/175; 355/3 DD 51 1111.121 G03g 13/08 581 Fieldof Search 118/637; 117/175; 355/15,

[56] References Cited UNITED STATES PATENTS 6/1962 118/637 3/1972 Ogawa118/637 1111 3,893,414 1451 July 8, 1975 [57] ABSTRACT An electrostaticcopying machine is provided utilizing a magnetic brush developmentsystem. The magnetic brush presents a band of developer to a latentelectrostatic image, the width of the developer band being changed inaccordance with the size of copy paper used. This is effected byutilizing a variable length magnet inside a non-magnetic rotatableroller which carries developer thereon. The length of the magnet isvaried in accordance with the size of the copy paper used to accordinglychange the length of the magnetic field emanating therefrom therebyeffecting a corresponding change in the bandwidth of the developertransported to the image. An alternate method for effecting the sameresult is to utilize a shunt which may be swung into a positionsurrounding one end of the magnet to prevent the magnet field emanatingfrom that end of the magnet from being effective to attract developer tothe roller thereby decreasing the developer bandwidth.

6 Claims, 6 Drawing Figures mes MTEFQ'TEDJUL 8 I975 SHEEI Iii/11111;

METHOD AND APPARATUS FOR VARYING DEVELOPER BANDWIDTH DESCRIPTION OF THEINVENTION In an electrostatic copier system. it has been found thatdeveloper (carrier and toner particles) life is related to the functionof the number of times the developer is cycled through the developmentsystem; the more times cycled, the shorter the life.

In known systems, it is the custom to present developer to aphotoconductive surface carrying a latent image over the same widthregardless of the size of the final image desired. For instance,developer may be presented to a surface carrying a latent image over a14-inch bandwidth for copying an image onto either an 11 X 14-inch paperor an 8V2X 1 linch paper. The bandwidth coincides with the length of thepaper as the paper is fed through the machine. For the latter sizepaper, developer is presented to a latent image over an extra 3-inchbandwidth and is, therefore, needlessly circulated with resultantshortening of developer life.

It is, therefore, an object of this invention to stop needlesscirculation of excess developer and thus improve developer life.

It is a further object of this invention to limit developer presentationto a surface carrying a latent image over a bandwidth equal to thelength of paper on which the developed image is to be transferred.

Furthermore, in some systems the photoconductive surface is developedbeyond the borders of an original and copy sheet resulting in removal ofexcess toner particles from the areas of the surface which taxes thecleaning system.

It is, therefore. an additional object of the invention to preventneedless cleaning of toner particles from a photoconductive surface.

Other objects of the invention will become apparent from the followingdescription with reference to the drawing wherein:

FIG. 1 is a schematic view of a copying apparatus; FIG. 2 is a viewtaken along section line 22 of FIG.

FIG. 3 is a view of modification of the embodiment of FIGS. 1 and 2;

FIG. 4 is a view taken along section line 44 of FIG.

FIG. 5 is a top view of a copy paper receptacle adjuster; and

FIG. 6 is a partial view taken along section line 6-6 of FIG. 5.

Referring to FIGS. 1 and 2, there is shown a drum 10 on which aphotoconductive layer 12 is formed. Arranged about the drum 10 are acharging station A, an imaging station B, a development station C, animage transfer and fixing station D and a cleaning station E. All of thefunctions of these stations are well known in the art. An electrostaticlatent image may be formed on the layer 12 and developed withxerographic toner particles. The invention resides in the developingstation to which particular attention is directed.

The development station comprises a developer sump 14 containingdeveloper 16 therein. The developer is a mixture of toner particles andferromagnetic carrier particles. The toner particles aretriboelectrically attached to the carrier particles. One side wall ofthe sump has a stationary hub I8 affixed thereto which receives one endof a cylinder or roller 20 therein which is of non-magnetic material.

A bearing race 22 is secured to the hub 18 to allow the cylinder 20 torotate relative to the hub and sump. The other end of the cylinder 20 isoperably secured to a motor (not shown) by a gear train (not shown) fordriving the cylinder. A keeper member 24 of magnetic material is securedto the hub l8 and has secured thereto a developer pickup magnet 26, adevelopment magnet 28 and a residual developer transport magnet 30, allof which are located within the confines of the cylinder 20. Attached tothe keeper 24 is a guide portion 31 having an upper surface 32, a lowersurface 34 and a side surface 36 surrounding the magnet 26 for purposesto be hereinafter described. The guide portion 31 is of a non-magneticmaterial and the magnets 26, 28 and 30 are permanent.

The magnet 26 is split into two sections, a stationary section 38 and aslidable section 40. Surfaces 42 and 44 of sections 38 and 40,respectively, are complementary to each other and slidably engage eachother. A leaf spring 46 is secured to the side wall 36 and engages theslidable section 40 to maintain the section 40 in contact with thesection 38. A flexible cable assembly is provided and comprises atubular sheath 48, secured at one end to the hub 18 and at the other endto a portion 50 of the copier frame, and a flexible twisted wire 52slidable within the sheath 48. The wire 52 is connected at one end tothe slidable magnet section 40 and the other end has a knob 54 which maybe manually engaged to slide the wire back and forth. Upon pushing theknob in, the wire 52 pushes the magnet section 40 inwards to the phantomposition to shorten the effective magnetic field emanating from themagnet 26. These movements are guided by the guide surfaces 32 and 34.The leaf spring 46 ensures engagement of the section 40 with section 38.Upon pulling the knob out, the wire 52 pulls the magnet section 40 backto the position as shown in FIG. 2.

The split magnet has its applicability to copiers in the followingmanner: Assume the axial length a' of fixed section 38 is 11 inches andthe axial length "b of movable section 40 is 3 inches and assume thecombined axial length of the magnets 28 and 30 is 14 inches. With thesection 40 in the full line position, shown in FIG. 2, the total lengthof the magnet 26 is 14 inches. As the roller 20 rotates in the directionof the arrow it will magnetically pick up developer material in themagnetic field of magnet 26 across a 14inch axial band and present al4-inch band of developer to the photoconductive surface 12. When thesection 40 is in the phantom position, as shown in FIG. 2, the totallength of the magnet 26 is 11 inches, thus decreasing the magnetic fieldemanating therefrom by 3 inches. As the roller 20 rotates in thedirection of arrow A, it will magnetically pick up developer material inthe magnetic field of magnet 26 across an 11-inch axial band and presentapproximately an 11-inch band (allowing for slight spreading) ofdeveloper to the photoconductive surface 12. The magnet 40 may also bemoved into positions intermediate the full line and phantom positionsshown in FIG. 2 wherein a developer hand between 11 and 14 inches may bepresented to the photoconductive surface 12.

The length of a copy sheet usually corresponds to the axial length of adeveloped image carried by a photoconductive drum. For instance, theimage may be over an ll-inch or a 14-inch axial length of the drum to betransferred to an 11-inch or a 14-inch length copy paper, respectively.Developer life is a function of circulation through the developmentsystem; the more times cycled, the shorter the life. Thus, if developeris presented to the photoconductor 12 over a 14-inch bandwidth when anll-inch image and copy sheet are used, a 3-inch bandwidth of developeris unnecessarily circulated resulting in shorter developer life.However, if the length of the magnet 26 is decreased so the roller 20will only pick up an 11-inch bandwidth of developer which is thenpresented to the photoconductor, only the necessary amount of developeris presented to the photoconductor resulting in an increase in developerlife. If an 13-inch length copy sheet is used, the section 40 may bemoved inwards one inch from its position shown in FIG. 2 by pushing theknob 54 accordingly. An indicator may be provided to guide an operatoron how far to move the knob for various paper sizes. Obviously, variouspaper sizes may be designed for by changing the length of and the numberof the stationary and movable sections of the pick-up magnet 26.

Referring to FIGS. 3 and 4, a modification of the embodiment of FIGS. 1and 2 is shown. The same elements as in the previous embodiment aredesignated with the same reference numeral with an a affixed thereto. Inthis embodiment, a shunt 100 is pivotally connected to the keeper member24a. A torsion spring 101 is wrapped around the pivot connection andurges the shunt in a clockwise direction to surround a permanent magnet103. The flexible wire 52a is wrapped around a pulley 104 and connectedat the other end to the shunt 100. The shunt may be approximately 3inches in axial length and is of a material, such as thin gauge steel,to decrease the axial length of the magnetic field of the magnetic bar103 by approximately 3 inches when the shunt is in the full linepositions shown in FIG. 3. If a l4-inch copy paper is used, the knob 54ais pulled out to lift the shunt 100 into the phantom position shown inFIG. 3 whereby the axial length of the magnetic field of the magneticbar 103 will extend the full length of the magnet, Le, 14 inches. If anll-inch copy paper is used, the knob 54a is pushed in which allowsspring 101 to rotate the shunt 100 in a clockwise direction into thefull line position shown in FIG. 3.

Obviously, any number of shunts could be used and the length thereofcould vary according to the results desired.

In the above embodiments, the magnetic bar section 40 and the shunt 100have been shown as being selectively manually actuated. However, thecable 52 or 52a may be connected to a selector which adjusts a papertray to the length of paper used. In this manner, the axial magneticfield of the pick-up magnet 26 or 103 will be automatically adjusted tocopy paper size when the paper tray is adjusted. FIGS. 5 and 6 show anoverall view of such a selector and the wire 52 or 52a could beconnected to a selector 200 depicted therein. For a detailed operationof the selector, reference is made to US. Pat. No. 3,251,594 (.l.W.Wagner), which discloses and describes a similar such selector 348. Thedescription of this patent is incorporated herein by reference.

While the pick-up magnet has been disclosed in a combined pick-up anddevelopment roller, the invention could be employed in a system usingany number of rollers; the main feature being to employ this inventionin a roller prior to the developer being presented to thephotoconductive surface. However, it will be most advantageous to employthe invention in the initial developer pick-up roller.

What is claimed is:

1. A copying machine comprising: a member having a developable imagethereon, a developer sump containing developer therein having magneticproperties, means for transporting a band of developer from said sump tothe image for developing the same, means for selectively changing thewidth of the developer band, a copy paper supply receptacle, means forchanging the size of said receptacle to accommodate various sizes ofcopy paper, said selective means being operably connected to said lastnamed means to be controlled thereby.

2. A copying machine comprising: a member having a developable imagethereon, a developer sump containing developer therein having magneticproperties, means for transporting a bandwidth of the developer fromsaid sump to the image for developing the same, said means comprising arotatable non-magnetic member surrounding at least one magnetic member,said magnetic member being so constructed to vary in length, and meansto selectively increase or decrease the length of said magnetic memberto effect a corresponding change in the magnetic field emanatingtherefrom thereby effecting a corresponding change in the bandwidth ofthe developer transported to the image.

3. The structure as recited in claim 2 further comprising a copy papersupply receptacle, means for changing the size of said receptacle toaccommodate various sizes of copy paper, said selective means beingoperably connected to said last named means to be controlled thereby.

4. A copying machine comprising: a member having a developable imagethereon; a developer sump containing developer therein having magneticproperties, means for transporting a band of developer from said sump tothe image for developing the same, said means comprising a rotatablenon-magnetic member surrounding at least one magnetic member; a shunt,said shunt being located adjacent one end of said magnetic member, meansfor moving said shunt into a position to surround one end of saidmagnetic member and for withdrawing said shunt from said position, saidshunt being of a material to prevent the magnetic field emanating fromthe end of the magnetic member surrounded thereby from being effectiveto attract developer to said non-magnetic member.

5. The structure as recited in claim 4 wherein said magnetic member issupported by a stationary support member, and means for pivotablyconnecting said shunt to said support member.

6. The structure as recited in claim 4 further comprising a copy papersupply receptacle, means for changing the size of said receptacle toaccommodate various sizes of copy paper, said means for moving saidshunt being operably connected to said last named means to be controlledthereby.

1. A copying machine comprising: a member having a developable imagethereon, a developer sump containing developer therein having magneticproperties, means for transporting a band of developer from said sump tothe image for developing the same, means for selectively changing thewidth of the developer band, a copy paper supply receptacle, means forchanging the size of said receptacle to accommodate various sizes ofcopy paper, said selective means being operably connected to said lastnamed means to be controlled thereby.
 2. A copying machine comprising: amember having a developable image thereon, a developer sump containingdeveloper therein having magnetic properties, means for transporting abandwidth of the developer from said sump to the image for developingthe same, said means comprising a rotatable non-magnetic membersurrounding at least one magnetic member, said magnetic member being soconstructed to vary in length, and means to selectively increase ordecrease the length of said magnetic member to effect a correspondingchange in the magnetic field emanating therefrom thereby effecting acorresponding change in the bandwidth of the developer transported tothe image.
 3. The structure as recited in claim 2 further comprising acopy paper supply receptacle, means for changing the size of saidreceptacle to accommodate various sizes of copy paper, said selectivemeans being operably connected to said last named means to be controlledthereby.
 4. A copying machine comprising: a member having a developableimage thereon; a developer sump containing developer therein havingmagnetic properties, means for transporting a band of developer fromsaid sump to the image for developing the same, said means comprising arotatable non-magnetic member surrounding at least one magnetic member;a shunt, said shunt being located adjacent one end of said magneticmember, means for moving said shunt into a position to surround one endof said magnetic member and for withdrawing said shunt from saidposition, said shunt being of a material to prevent the magnetic fieldemanating from the end of the magnetic member surrounded thereby frombeing effective to attract developer to said non-magnetic member.
 5. Thestructure as recited in claim 4 wherein said magnetic member issupported by a stationary support member, and means for pivotablyconnecting said shunt to said support member.
 6. The structure asrecited in claim 4 further comprising a copy paper supply receptacle,means for changing the size of said receptacle to accommodate varioussizes of copy paper, said means for moving said shunt being operablyconnected to said last named means to be controlled thereby.